This disclosure relates to check valves, and more particularly, to check valves of the type having a deflectable membrane which is self-actuated when subject to forward fluid flow and closed when subject to a backward flow.
Check valves are passive devices that, by virtue of a deflectable element which functions as a diaphragm, open and close based on fluid flow direction, pressure and force therethrough. Such check valves are particularly useful in microfluidic systems, such as micro pumps, for directing fluid flow.
Ring mesas, cantilevers, and membranes fabricated from silicon, silicone, polyimide and metal have been used to form a deflectable valving element in check valves. In every micro-check-valve configuration, there is a valve seat and an orifice that is formed therein. The valve seat is often made of potassium hydroxide (KOH)xe2x80x94etched trapezoidal structures on a silicon substrate. Many check valves use a two-piece bonded construction that requires greater packaging labor. A two-piece bonded construction, however, is characterized by higher withstand forward and backward fluid working pressures.
A micro check valve configuration must generally satisfy performance criteria established by the designer. A number of criteria go into selecting and sizing a micro check valve. It is important to avoid excessive flow resistance which could lead to large pressure losses due to the micron-size property of the fluid directing orifice and the limited fluid passage property of the small gap between the deflectable valving element and the valve seat often.
In addition, the inherently small size of a micro valve attributes to stiction and surface tension effects between the valve seat and deflectable valving element. Cracking pressure, the minimum pressure to open a check valve during forward fluid flow, is commonly used to gauge the stiction effect. A micro check valve should have low cracking pressure, low membrane-induced flow resistance, small reverse leakage and large operational reverse pressure characteristics. Ideally, a single chip construction is also preferable to enjoy the benefits of reduced packaging demands.
The present disclosure describes a Parylene micro check valve and fabrication process therefore. The check valve includes a valve seat with a preferably roughened top surface to which a membrane cap is anchored by circumferentially-orientated twist-up tethers.
The micro check valve is found to exhibit low cracking pressure, high reverse pressure, low reverse flow leakage, and negligible membrane-induced flow resistance characteristics when used as a valve over a micro orifice through which flow liquid and gas fluids.
The invention takes advantage of BrF3 gas phase silicon etching and Parylene deposition to enable a low temperature fabrication process.